Stable, concentrated solutions of high molecular weight polyaniline and articles therefrom

ABSTRACT

Stable, concentrated solutions of high molecular weight polyaniline. In order to process high quality fibers and other articles possessing good mechanical properties, it is known that solution concentrations of the chosen polymer should be in the range from 15-30% (w/w). Moreover, it is desirable to use the highest molecular weight consistent with the solubility properties of the polymer. However, such solutions are inherently unstable, forming gels before processing can be achieved. The present invention describes the addition gel inhibitors (GIs) to the polymer solution, thereby permitting high concentrations (between 15% and 30% (w/w)) of high molecular weight ((M w )&gt;120,000, and (M n )&gt;30,000) emeraldine base (EB) polyaniline to be dissolved. Secondary amines have been used for this purpose in concentrations which are small compared to those which might otherwise be used in a cosolvent role therefor. The resulting solutions are useful for generating excellent fibers, films, coatings and other objects, since the solutions are stable for significant time periods, and the GIs are present in too small concentrations to cause polymer deterioration. It is demonstrated that the GIs found to be useful do not act as cosolvents, and that gelation times of the solutions are directly proportional to the concentration of GI. In particular, there is a preferred concentration of GI, which if exceeded causes structural and electrical conductivity degradation of resulting articles. Heating of the solutions significantly improves solubility.

This invention was made with government support under Contract No.W-7405-ENG-36 awarded by the U.S. Department of Energy. The governmenthas certain rights in the invention.

This application is a continuation of application Ser. No. 08/658,928filed on May 31, 1996, now abandoned.

FIELD OF THE INVENTION

The present invention relates generally to the preparation of solutionsof polyaniline and, more particularly, to the preparation ofconcentrated solutions (between 15% and 30% (w/w) having molecularweights with weight averages (M_(w))>120,000 and number averages(M_(n))>30,000 in the emeraldine base form of polyaniline, which may beprocessed into films, coatings, and fibers that are highly electricallyconducting after subsequent exposure to acid.

BACKGROUND OF THE INVENTION

Dopable p-conjugated polymers (alternating double and single bonds alongthe polymer main chain repeat units), such as those found in the familyof polymers known as polyaniline, show potential for a variety ofcommercial applications such as chemical separations, electromagneticinterference shielding, protection of metals from corrosiveenvironments, antistatic coatings, and current-carrying fibers.Polyaniline is a commercially attractive polymer since, unlike manyother dopable p-conjugated polymers, it is both environmentally stableand can be made electrically conducting by acid treatment.

Electrical conductivity (σ) of π-conjugated polymers is physicallypossible due to electron mobility along (intrachain) and between(interchain) polymer chains in a solid-state article. The magnitude ofthe conductivity depends upon the number of charge carriers (n) which isdetermined by the extent of doping with oxidizing or reducing chemicalagents (or in the special case of polyaniline, with an acid), the chargeon these carriers (q), and on the combined interchain and intrachainmobilities (μ). These relationships are related by:

    σ=n q μ

In order to obtain high conductivities, n is usually maximized by achemical doping process (generation of electrons or holes on the polymerchain), so that conductivity becomes dependent on the mobility of thecarriers. At the maximum doping levels, it is the mobility of the chargecarriers which must be increased to obtain higher conductivity. Mobilityof charge carriers in some cases depends upon the polymer's morphologyonce it is "frozen" into a nonequilibrium glassy solid state articledetermined by processing conditions. Interchain mobility depends uponthe statistical distribution of conformational features such as bond andtorsion angles, interchain distances, packing density, orientation,fractional crystallinity, free volume, etc. On the other hand,intrachain mobility depends upon the degree and extent of π-conjugationand defects along the polymer chains, and the polymer chainconformations. It is therefore desirable to develop improved processingprocedures which allow control over the factors governing mobility inorder to generate higher conductivities in polyaniline.

Polyaniline in its most useful and environmentally stable oxidationstate is given the name emeraldine base (EB). The untreated EB is itselfan electrical insulator composed of tetrameric repeating units eachcontaining two secondary amine and two tertiary imine nitrogen atoms asshown in FIG. 1a hereof. When powders of EB are treated with acidsolutions, the imine nitrogen atoms extract protons from solution withthe acid counterion associating with the polymer chain to maintainoverall charge neutrality. When less than 50% of the available iminenitrogens are coordinated to form quaternary iminium salt complexes,i.e., immersion in pH's between 2 and 7, the polymer becomes asemiconductor and is called a bipolaron (See FIG. 1b hereof), sincecharge carriers delocalized along the π-conjugated polymer backbone arespinless. Immersion in more concentrated acid solutions (pH<2) generatespolarons (See FIG. 1c hereof) since, due to self-localizedreorganization of electronic states, the mobile charge carriers are nowsufficiently delocalized to produce mobile spins. Thus, treatment of EB(which has a conductivity of less than 10⁻¹⁰ Siemen/cm [S/cm]) with anexcess of concentrated acid solution (pH<1) results in an electricallyconductive polymer having a conductivity of about 1 S/cm. Under theselatter doping conditions, the maximum number of charge carriers (n) havebeen generated on the polymer since all of the nitrogen atoms, availableas protonation sites, are occupied.

The commonly reported polyaniline synthesis describes the heterogeneousradical chain polymerization of aniline at 0° C. in 1 N aqueous HCl, andleads to the acid salt form of polyaniline (See e.g., A. G. MacDiarmidet. al., "Conducting Polymers", Alcacer, L., ed., Riedel Pub., 1986,p.105, FIG. 1c). When this polyaniline powder is immersed in an excessof a strong aqueous base, it is deprotonated to yield EB (See FIG. 1ahereof). Most polyaniline investigations have employed materials havingmolecular weights with weight average (M_(w))<100,000 and number average(M_(n))<30,000 which are produced by these synthetic conditions (See,e.g., E. J. Oh et al., "Polyaniline: Dependency Of Selected PropertiesOn Molecular Weight," Synthetic Metals, 55-57, 977 (1993).

In U.S. Pat. No. 5,312,686 for "Processable, High Molecular WeightPolyaniline And Fibers Made Therefrom," which issued to Alan G.MacDiarmid et al. on May 17, 1994, a procedure for preparing highmolecular weight polyaniline is reported. The method involves reducingthe standard reaction temperature to -30° C., by adding 5 M LiCl to thereaction mixture, thereby producing high-molecular-weight EB. Themolecular weight of the resulting polymer may be varied from(M_(w))=250,000 to greater than (M_(w))=400,000 by controlling the rateat which the initiator is added to the cold reaction mixture, and thereaction temperature. These high molecular-weight polyanilines exhibitpoor solubility and have short gelation times. A complex cyclingprocedure of acid doping, followed by undoping with aqueous basereportedly led to improved solubility and concentrated solutions inN-methyl-2-pyrrolidinone (NMP). Unfortunately these solutions werediscovered to rapidly gel when prepared in the 1-3% w/w range in NMP.Thus, there exists a need for developing procedures to process highmolecular weight polyaniline.

The utility of polyaniline EB with (M_(w))>100,000 and (M_(n))>30,000has been limited. However, in order to process high quality fiberspossessing good mechanical properties, it is known in the art thatsolution concentrations of a particular polymer should be in the 15-30%(w/w) range. Moreover, it is desirable to use the highest molecularweight polymers that will dissolve in solvents in the targetconcentration range. Tensile strength and modulus, flex life, and impactstrength all increase with increasing molecular weight. Typically,molecular weights (M_(w))>120,000 and (M_(n))>30,000 are preferred. Suchsolutions are suitable for dry-wet or wet-wet fiber spinning processesthat produce high quality fibers, and also for the generation of films,coatings and other useful objects.

The EB form of polyaniline is reported to be soluble in NMP at the 1-5%weight level. Such solutions may be cast into dry dense films after thewet film is thermally treated to remove the solvent. Films prepared inthis manner, when immersed in a concentrated acid solution, have aconductivity of between 1 and 5 S/cm. Few other organic solvents for EB,such as N,N,N'N'-tetramethyl urea and N,N'-dimethyl-propylene urea(DMPU) as examples, have been reported in the literature. All of thesesolvents have carbonyl functional groups, which tend to form stronghydrogen bonds between the carbonyl group of the solvent and thesecondary amine groups of EB, thus encouraging limited solubility atdilute concentrations prepared from low molecular weight polymer.However, solubilities of even low molecular weight EB (0° C. synthesis,(M_(w))<100,000, (M_(n))<30,000) in such solvents is poor (<1-5% w/w).Solutions prepared from NMP above this concentration range exhibit rapidgelation. (See, e.g., E. J. Oh et al., supra). Oh et al. observed thatthe gelation time is both inversely proportional to the weight percentof EB in NMP and to its molecular weight. S. A. Chen et al. in"Conductivity Relaxation Of 1-Methyl-2-Pyrrolidinone-PlasticizedPolyaniline Film", Macromolecules 28, 7645 (1995), have reportedevidence for a strong hydrogen bond interaction of the C═O group fromNMP with the secondary amine (NH) functional groups of EB. Presumably,it is the imine nitrogens from the polymer which are strongly attractedto hydrogen atoms of the secondary amines on adjacent chains. Thisstrong attractive force promotes interchain hydrogen bonds which serveas physical cross-links between chains and leads to rapid gelation in EBsolutions, or in the solid-state article (FIG. 2a).

Emeraldine base solutions can be processed into free-standing films. Ifsuch films are stretched over a hot pin before immersion in aconcentrated acid solution, and then subsequently treated with an acid,conductivities of as great as 200 S/cm may be obtained. A. G. MacDiarmidet al., "Towards Optimization of Electrical and Mechanical Properties ofPolyaniline: Is Cross-Linking Between Chains the Key?", SyntheticMetals, 55-57, (1993) 753, shows that stretch alignment of EB films[prepared from dilute (1-3% w/w) EB in N-methyl-2-pyrolidinone (NMP)solutions], over a hot pin at 120° C. to a 2-5× draw ratio, increasesthe films fractional crystallinity (from ˜5 to 50%) and additionallyincreases the anisotropic conductivity of the maximally acid doped filmfrom 1 to 200 S/cm, in the direction parallel to the stretch. Hence,this example demonstrates the importance of manipulating the parameterswhich control carrier mobility (μ) in the solid-state articles toenhance physical properties such as conductivity.

Some researchers have reported preparation of EB solutions having >10%w/w from DMPU (See e.g., K. T. Tzou, R. V. Gregory, "Improved SolutionStability And Spinnability Of Concentrated Polyaniline Solution UsingN,N-DimethylPropylene Urea As The Spin Bath Solvent" Synthetic Metals69, 109-112, 1995). Here also, the investigators employed a syntheticprocedure which yields low molecular weight EB ((M_(w))<100,000,(M_(n))<30,000). The solutions were stable long enough for the authorsto spin a fiber which exhibited high conductivity; however, the detailsof processing and the solubility limits are lacking, and the resultingmechanical properties of the fiber would be much improved if highermolecular weights were accessible in their solvent systems.

A second category of reported solvents for polyaniline includes acids,such as m-cresol, formic acid, methanesulfonic acid, sulfuric acid, asexamples. Solubility derives from the basic nature of the EB polymerwhich forms ionic coordination complexes between the acid and the iminenitrogens of the polymer. Solubility increases as the strength of theacid increases (>10% w/w for sulfuric acid, 1-5% w/w in m-cresol andformic acid). It is doubtful that EB is truly dissolved in such acidsolutions; rather, it is more likely that the solutions consist of afine dispersion of polyaniline particles. Processing EB in suchsolutions is not desirable since 1. The solvents are hazardous; 2.Strong acids can either over-oxidize emeraldine or chemically substituteon the polymer rings; and 3. The resulting polymers tend to degrade ifstored in solution for more than a few days. Additionally, even thoughpartially soluble in acid media, EB fibers spun from acid solution havebeen found to be mechanically weak.

A major obstacle to the fabrication of commercially useful articles,such as high quality fibers, hollow fibers, or articles having otheruseful geometries, from solutions of polyaniline, therefore, is the poorsolubility of the polymer in solvents suitable for processing usingconventional polymer engineering methods. Such solutions exhibit astrong tendency to form gels on a relatively short time scale due tointerchain hydrogen bond formation, even for dilute solutions. Theinstability is such that the solutions cannot be extruded throughspinnerette orifices because they gel too rapidly or form particulatematerial which clogs the spinnerette tip, causing unsafe pressureincreases in the spin line which represent a significant health risk tooperators.

U.S. Pat. No. 5,135,682, for "Stable Solutions Of Polyaniline And ShapedArticles Therefrom, which issued to Jeffrey D. Cohen and Raymond F.Tietz on Aug. 4, 1992, discloses a procedure for preparing stabledry-wet spinning solutions of EB in the 10-30% w/w range. Stable,spinnable solutions were prepared using 1,4-diaminocyclohexane,1,5-diazabicyclo (4.3.0) non-5-ene, or by dissolving EB in NMP with theaddition of specified quantities of cosolvents consisting of eitherpyrrolidine (Py) [11% EB; 33% Py; and 56% NMP w/w/w] or ammonia. Theamount of pyrrolidine added as cosolvent, compared to the amount of theEB added to NMP solution, can be expressed as the ratio of molesPy/moles EB tetrameric repeat unit, which in their preferred embodimentis 15.5. (The molecular weight of the EB repeat unit is 362 g/mol, andthat of Py is 71.13 g/mol). Poor quality fibers were observed for theNMP/Py solutions (See, e.g., ibid., Example 5). The work was furtherdescribed in "Polyaniline Spinning Solutions and Fibers," by C. -H. Hsu,J. D. Cohen and R. F. Tietz, in Synthetic Metals 59, 37 (1993), wherethe authors suggested that the physical degradation of the polyanilinefibers, especially after exposure to an acid, was likely due to theaddition of Py or ammonia cosolvents, as a result of chemicalinteractions between the cosolvent and the polymer. Molecular weightsreported from the described synthetic procedure were approximately(M_(n))=20,000 and (M_(w))=120,000. Synthetic conditions were carriedout at -8° C. without LiCl added to the reaction mixture.

In U.S. Pat. No. 5,147,913, for "Cross-Linked Polymers Derived FromPolyaniline And Gels Comprising The Same," which issued to Alan G.MacDiarmid and Xun Tang on Sep. 15, 1992, the preparation ofcross-linked polymers of polyaniline by providing a substantially linearpolymer which comprises polyaniline and/or a polyaniline derivative,admixing the linear polymer with a liquid in which the cross-linkedpolymer is substantially insoluble, and cross-linking the polymerthrough agitation, is described. Preferred liquids for preparing suchgels include NMP. A preferred embodiment for forming such gels isutilization of EB in NMP at concentrations >5% w/w.

In "Stabilization of Polyaniline Solutions," by Debra A. Wrobleski andBrian C. Benicewicz, Polymer Preprints 35, 267 (1994), the authorsreport the addition of hindered amine antioxidants and UV absorbers toup to 5% w/w solutions of EB in NMP to increase the gelation time forsuch solutions. Although molecular weights for the EB are not reported,the described synthesis must have produced EB with weight averagemolecular weights below (M_(w))<100,000 and number averages(M_(n))<30,000.

Accordingly, it is an object of the present invention to provide amethod for dissolving high concentrations (between 15% and 30% w/w) ofhigh molecular weight polyanilines (weight averages (M_(w))>120,000 andnumber averages (M_(n))>30,000) without significant gel formation over atime period sufficient to process the solution obtained thereby intoarticles.

Another object of the invention is to provide a method for preparingsolutions having high concentrations (between 15% and 30% w/w) of highmolecular weight polyanilines ((M_(w))>120, 000 and (M_(n))>30, 000)from which articles can be prepared having improved electricalconductivities and mechanical properties.

Additional objects, advantages and novel features of the invention willbe set forth in part in the description which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and attained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

SUMMARY OF THE INVENTION

To achieve the foregoing and other objects, and in accordance with thepurposes of the present invention, as embodied and broadly describedherein, the method for preparing solutions having between 15% and 30% byweight of (M_(w))>120,000, (M_(n))>30,000 emeraldine base form ofpolyaniline hereof includes: mixing a solvent for polyaniline with asecondary amine such that the molar ratio of secondary amine topolyaniline tetramer repeat unit is between 0.1 and 5.0, forming therebya solution; and dissolving the polyaniline in the solution thusprepared.

In another embodiment of the invention, in accordance with its objectsand purposes, as embodied and broadly described herein, the method forpreparing solutions having between 15% and 30% by weight of(M_(w))>120,000, (M_(n))>30,000 emeraldine base form of polyanilinehereof includes: dissolving a chosen amount of polyaniline in abifunctional solvent therefor having both an amide group and a secondaryamine group, forming thereby a solution.

In yet another embodiment of the invention, in accordance with itsobjects and purposes, as embodied and broadly described herein, themethod for preparing polyaniline fibers hereof includes: preparing asolution having between 15% and 30% by weight of (M_(w))>120,000,(M_(n))>30,000 emeraldine base form of polyaniline by mixing a solventfor polyaniline with a secondary amine such that the molar ratio ofsecondary amine to polyaniline tetramer repeat unit is between 0.1 and5.0, forming thereby a solution, and dissolving a chosen quantity ofpolyaniline in the solution thus prepared; extruding the solution toform a fiber; passing the extruded fiber through an air gap; conveyingthe fiber through a coagulation bath, wherein the fiber cools andsolidifies and wherein the solvent and gel inhibitor are removed; anddrying the cooled and solidified fiber.

In still another embodiment of the invention, in accordance with itsobjects and purposes, as embodied and broadly described herein, themethod for preparing polyaniline fibers hereof includes: preparing asolution having between 15% and 30% by weight of (M_(w))>120,000,(M_(n))>30,000 emeraldine base form of polyaniline by dissolving achosen amount of polyaniline in a bifunctional solvent therefor havingboth an amide group and a secondary amine group; extruding the solutionto form a fiber; passing the extruded fiber through an air gap (dry-wet)or no air gap (wet-wet); conveying the fiber through a coagulation bath,wherein the fiber cools and solidifies and wherein the solvent and gelinhibitor are removed; and drying the cooled and solidified fiber.

In another embodiment of the invention, in accordance with its objectsand purposes, as embodied and broadly described herein, the method forpreparing polyaniline films hereof includes: preparing a solution havingbetween 15% and 30% by weight of (M_(w))>120,000, (M_(n))>30,000emeraldine base form of polyaniline by mixing a solvent for polyanilinewith a secondary amine such that the molar ratio of secondary amine topolyaniline tetramer repeat unit is between 0.1 and 5.0, forming therebya solution, and dissolving a chosen quantity of polyaniline in thesolution thus prepared; coating a substrate with the solution; andthermally annealing the coated substrate.

In yet another embodiment of the invention, in accordance with itsobjects and purposes, as embodied and broadly described herein, themethod for preparing polyaniline films hereof includes: preparing asolution having between 15% and 30% by weight of (M_(w))>120,000,(M_(n))>30,000 emeraldine base form of polyaniline by dissolving achosen amount of polyaniline in a bifunctional solvent therefor havingboth an amide group and a secondary amine group; coating a substratewith the solution; and thermally annealing the coated substrate.

In still another embodiment of the invention, in accordance with itsobjects and purposes, as embodied and broadly described herein, themethod for preparing polyaniline films hereof includes: preparing asolution having between 15% and 30% by weight of (M_(w))>120,000,(M_(n))>30,000 emeraldine base form of polyaniline by mixing a solventfor polyaniline with a secondary amine such that the molar ratio ofsecondary amine to polyaniline tetramer repeat unit is between 0.1 and5.0, forming thereby a solution, and dissolving a chosen quantity ofpolyaniline in the solution thus prepared; coating a substrate with thesolution; immersing the coated substrate into a non-solvent bath,whereby the polyaniline precipitates forming a film; and drying thefilm.

In another embodiment of the invention, in accordance with its objectsand purposes, as embodied and broadly described herein, the method forpreparing polyaniline films hereof includes: preparing a solution havingbetween 15% and 30% by weight of (M_(w))>120,000, (M_(n))>30,000emeraldine base form of polyaniline by dissolving a chosen amount ofpolyaniline in a bifunctional solvent therefor having both an amidegroup and a secondary amine group; coating a substrate with thesolution; immersing the coated substrate into a non-solvent bath,whereby the polyaniline precipitates forming a film; and drying thefilm.

Benefits and advantages of the present invention include the preparationof stable, particle-free solutions suitable for producing high qualityarticles therefrom from noncaustic and recoverable solvents.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe specification, illustrate the embodiment(s) of the present inventionand, together with the description, serve to explain the principles ofthe invention. In the drawings:

FIG. 1 is a schematic representation of the repeat unit for polyaniline,where FIG. 1a illustrates the EB form thereof, FIG. 1b illustrates thesemi-conducting (bipolaron) form obtained by immersion of the polymer inacid solutions having a pH in the range between 7 and 2, while FIG. 1cillustrates the highly conducting (polaron) form obtained by immersionof the polymer in acid solutions having a pH<2.

FIG. 2 is a schematic representation of interchain hydrogen bonding inEB, FIG. 2a illustrating the interaction between imine nitrogens on onechain and the hydrogen atom bonded to the secondary amine of an adjacentchain, while FIG. 2b illustrates one of the gel inhibitors (GIs) of thepresent invention, 2-methylaziridine, forming hydrogen bonds with theimine nitrogens of a solvated EB chain, thereby inhibiting theinterchain polymer associations through the hydrogen bond formationmechanism illustrated in FIG. 2a, hereof, and further forming adielectric shield by screening the imine nitrogens, thereby producingenhanced solubility in the presence of a solvent such asN-methyl-2-pyrrolidinone (NMP).

FIG. 3 is a graph of gelation time as a function of the molar ratio ofGI to EB repeat unit for 2-methylaziridine and pyrrolidine GIs at 60°C., illustrating that higher GI/EB ratios generate longer gelationtimes.

FIG. 4 is a graph of electrical conductivity as a function of the molarratio of GI to EB repeat unit for 2-methylaziridine and pyrrolidine GIsat 20° C., illustrating that higher GI/EB ratios result in degradationof mechanical properties of resulting thermally annealed films and thatcertain GIs yield significantly reduced bulk electrical conductivitiesin such articles.

FIG. 5 shows an EB fiber prepared from a stable 20% (w/w) solution bydry-wet spinning having been tied in a knot which demonstratessubstantial mechanical strength, such fibers, after stretch alignmentand acid doping being observed to have electrical conductivities >20S/cm.

DETAILED DESCRIPTION

Briefly, the present invention includes the addition of gel inhibitors(GIs) to solutions of EB in order to permit high concentrations (between15% and 30% (w/w)) of high molecular weight polyanilines((M_(w))>120,000, and (M_(n))>30,000) to remain stable and particle-freefor sufficient time to fabricate desired articles therefrom. Forexample, production of high quality fibers possessing good mechanicalproperties requires concentrations of the chosen polymer in the 15-30%(w/w) range. It is demonstrated that the GIs found to be useful do notact as cosolvents, and that gelation times of the solutions are directlyproportional to the concentration of GI. In particular, there is apreferred concentration of GI, which if exceeded causes structural andelectrical conductivity degradation of resulting articles. Heating ofthe solutions significantly improves solubility.

Reference will now be made in detail to the present preferredembodiments of the invention. As stated hereinabove, NMP,N,N,N'N'-tetramethylurea, and DMPU are the best known solvents for EB.Higher concentrations of EB(>5% w/w) in such solvents lead to rapidgelation due to strong intermolecular H-bonding between polyanilinechains, and decreases in the solubility of EB are directly related toincreases in the molecular weight of the polymer. The interactionbetween the amine functionality of the EB tetramer repeat unit and thecarbonyl (C═O) or phosphonyl (P═O) or sulfonyl (S═O) groups of thesesolvents is thought to be responsible for the solubility of thismaterial in such solvents. It is important to note that the iminenitrogens are not presumed to be hydrogen bonded with the solventmolecules. If the solute concentration is <2% w/w, intermolecularH-bonding between EB molecules is less likely to occur in view of theincreased spacing between the molecules. Thus, such solutions remainstable and particle-free for a significant amount of time. However, asthe concentration is increased, EB molecules become more closelydisposed and a number of the secondary amine nitrogens unbonded by thesolvent may H-bond to the imine nitrogens between adjacent polymerchains. See, e.g., FIG. 2a hereof. Gelation will then occur in ashortened time period, and stable, particle-free solutions becomedifficult to prepare. It is recognized that for EB molecular weightsM_(w) >100,000, such H-bonding may occur in very short times forsolutions having <1% w/w of EB.

An approach to this problem, according to the teachings of the presentinvention, is to introduce a gel inhibitor to the solutions as anadditive which subsequently complexes with the tetramer repeat unitimine nitrogens, thereby providing a "dielectric shield" which inhibitsthe natural tendency for EB chains to aggregate and gel at highconcentrations by formation of interchain imine-amine hydrogen bonds.See, e.g., FIG. 2B hereof. Such additives are used in small amounts in arange of molar ratios of GI to EB tetramer repeat unit of 0.1 to 5.0,and more preferably in the range of 0.5 to 3.0, and most preferably inthe range from 1 to 2. Greater quantities of gel-inhibitors, as might beused if one were using cosolvents, have been found to seriouslydeteriorate the resulting polymer articles by embrittlement. This isespecially true following doping with an acid after thermal evaporationof the solvent, so as to render the article conductive. An article withpoor mechanical properties and/or significantly reduced conductivitiesresults. Films, fibers, and/or other articles disclosed by the presentinvention can be prepared by immersion precipitation (IP) into anonsolvent coagulation bath and thereby retain excellent mechanicalproperties, e.g., flex, modulus, etc., and may also be rendered highlyconductive after exposure to an acid.

The preparation of polyaniline used in these experiments is nowdescribed. Such high molecular weight materials are also readilyprepared by emulsion polymerization procedures (See Y. Cao and J.Osterholm, "Electrically Conducting Polyaniline: Method for EmulsionPolymerization", U.S. Pat. No. 5,324,453, issued 1994.). The solubilitycharacteristics of these high molecular weight polyaniline emeraldinebases behave identically to those described herein.

High molecular weight polyaniline is synthesized at -45° C. using acyclohexanone/CO₂ ice bath. In a typical reaction, 100 g (1.074 mole) ofaniline were dissolved in 1500 ml of 1M HCl and aqueous 5 M LiClsolution. The solution was transferred to a 4 L resin kettle, andsubsequently immersed in a cyclohexanone/CO₂ ice bath, where it wasmechanically stirred throughout the course of the reaction. After 1 h.the reaction temperature of the aniline solution reached a temperatureof -45° C. Ammonium persulphate [131 g (0.574 mole)] was dissolved in aseparate flask which contained 1200 ml of 1M HCl and 5M LiCl solution atroom temperature. This oxidant solution was added to the anilinesolution at a rate of 8 mL/min. by means of a metered syringe pump.Thirty minutes after the first additions of ammonium persulphatesolutions the reaction mixture appeared pink in color, changing tointense orange after about 3 h. Twenty-four hours later, the solutionwas bluish green in color, indicating the formation of doped polyanilinein its emeraldine hydrochloride form (FIG. 1c). The reaction mixture wasleft with continuous vigorous stirring at -45° C. for an additional 48h. At that time the temperature of the reaction mixture was allowed toslowly increase to 0° C. The resulting polyaniline emeraldinehydrochloride powder occupied the entire volume of the reaction flask,and it appeared very bulky and fibrous as compared to polyanilineemeraldine hydrochloride powders prepared at 0° C. without LiCl.

The emeraldine hydrochloride powder was collected by vacuum filtrationand subsequently washed with 2 L increments of 1M HCl until the filtratebecame colorless. The powder was then washed with 2 L of water andtransferred to a 4 L beaker containing 2.5 L of 0.1N NH₄ OH solution,stirred for 1 h., and subsequently vacuum filtered to collect thedeprotonated EB powder (FIG. 1a). The polymer was reacted with another2.5 L of 0.1 N NH₄ OH aqueous solution for another hour, andsubsequently vacuum filtered to recover the EB powder. The EB polymerwas dried under dynamic vacuum at 10⁻² torr for more than 72 hours toremove residual water. Polymer yields were typically 40 to 45%. Anidentical synthetic procedure was performed at a slightly higherreaction temperature of -15° C. utilizing a polyethylene glycol/dry iceslurry as the cooling bath.

The molecular weight of polyaniline synthesized at -15° C. and --45° C.in 5M LiCl/1M HCl have similar molecular weights as indicated in Table 1which shows gel permeation chromatography (GPC) results for highmolecular weight polyanilines synthesized under the varying conditionsdescribed above. The measurements of molecular weight were performedusing GPC on 0.1% (w/w) solutions of EB in NMP at room temperature witha linear column with a UV detector monitoring 320 nm transmitted light.Molecular weights were derived from polystyrene standards analyzed underidentical elution conditions. The polydispersity of the samples (M_(w)/M_(n)) was difficult to determine accurately due to poorchromatographic resolution of the bimodal peak distributions.

                  TABLE 1                                                         ______________________________________                                        Sample  Synthetic Conditions                                                                            M.sub.n M.sub.w                                     ______________________________________                                        1       -15° C., 5M LiCl,                                                                        33,371  618,614                                        1M HCl                                                                       2 -15° C., 5M LiCl, 67,016 680,501                                      1M HCl                                                                       3 -45° C., 5M LiCl, 70,033 494,785                                      1M HCl                                                                     ______________________________________                                    

It is known that the GPC analysis of the synthesized EB (EB) in NMPsolution has a bimodal molecular weight distribution. This is likely dueto the aggregation of the polyaniline in the NMP. Such phenomenon may beresolved by adding the LiCl to the NMP solution. The GPC resultspresented in Table 1 were obtained without the addition of LiCl to theNMP solutions for comparison to known reference chromatograms. It isclear that each of the polyaniline samples is of high molecular weight,(M_(w))>120,000 and (M_(n))>30,000. It is also apparent that themolecular weight of these samples is significantly higher than thepolyaniline synthesized at 0° C. (See M. Angelopoulos, et al, "LiClInduced Morphological Changes in Polyaniline Base and Their Effect onthe Electronic Properties of the Doped Form", Macromolecules, 29, 8,3046) without LiCl added to depress the freezing point of water in thereaction mixture, as is most frequently cited in the literature.

It is a simple undertaking to survey additional compounds for theirutility as gel inhibitors and/or solvents which are not presently setforth herein. It is similarly straightforward to determine which gelinhibitors and solvents do not perform well. Those skilled in the artwill appreciate the simplicity of the following gel inhibitor (or newsolvent) rapid screening procedure. Typically, the weight of a newpotential gel inhibitor (GI) is adjusted to give a GI/EB mole ratio ofabout 0.5-3.0 in a known (or candidate) solvent. The GI and solventmixture is placed in an oven at 60° C. for 10 min. in a tightly sealedchemically resistant polytetrafluroethylene (PTFE) container. It ispossible to perform this screening with candidate gel inhibitors orsolvents at temperatures up to the decomposition temperature of the EB(˜320° C.). Sufficient EB powder is then rapidly added to the mixturewith vigorous stirring and returned to the oven for 5 min. timeintervals. After several short heating intervals (with repetitivestirring), if a fluid, particle-free flowable liquid is obtained, then aviable gel inhibitor (or solvent) has been identified. The solution issubsequently spread onto two separate glass, metal, ceramic, or plasticplates, and formed into flat wet film sheets of desired thickness bymeans of a gardener blade. One plate is subjected to a 120° C.convective oven for 1-2 h. (a thermally annealed film or coating), whilethe other is immediately immersed into a polymer nonsolvent bath(typically water) for more than 10 h. (an IP film).

The respective as cast thermally annealed films (or coatings) may thenbe immersed in any desirable pH solution for several hours, removed andair dried. A standard four point probe method (See Vander Pauw, L. J.Phillips Technical Review 20, 220 (1958)) for determining the bulkelectrical conductivity is employed. The thickness of the porous film isgenerally adjusted in the range from 2 to 4 mil (50-100 micron). Afterit is removed from the nonsolvent bath, such films are immersed into 1 NHCl for 1 h. These films have a short time lag to achieve the maximallydoped state. The thermally cured dense films require longer dopingintervals, presumably due to their lower fractional free volumes. Afterthe films are removed from the acid solution, they are wiped dry and airdried for ˜1 h., and conductivity measurements are taken.

The mechanical integrity of an acid-doped film is generally determinedby a simple flex test: if the film can be manually flexed 180° withoutbreaking, it is considered to be flexible (F); if it fractures or breaksit is considered brittle (B). If the film or coating does not easilydelaminate during the peel off from the casting substrate, and if thefilm or coating substrate is scratched from the perimeter with a razorblade so that the polymer flakes or shatters into pieces, it isconsidered very brittle (VB). If the film (especially IP films) can bemanually flexed between 900 to 1800 without breaking, it is consideredsomewhat flexible (SF). Similarly, when surveying fibers preparedaccording to the teachings of the present invention, an initial test ofmechanical integrity is the ability of the fiber to be tied into a knot(FIG. 5).

More sophisticated electrical and mechanical testing may follow therapid screening procedure described above, or it may be desirable, forinstance, to vary the GI/EB molar ratio in the preferred range of thepresent invention; however, the simplicity of the aforementionedprocedure has allowed the present inventors to rapidly determine thatthe following compounds were not effective gel inhibitors: aniline,N-methylpyrrolidine, pyrrole, pyridine,1,1,1,3,3,3-hexafluoro-2-propanol. Similarly, it was found by thismethod that the following compounds were not effective solvents whenused with exemplary gel inhibitors of the present invention:1-methyl-4-piperidone, m-cresol, tetramethylene sulfone, glycol sulfite,p-xylene, 1,2-dichlorobenzene, dimethylformamide (DMF), formamide,tetrahydrofuran, triethylphosphate, N-methylacetamide, poly(ethyleneglycol), dichloromethane, toluene, water, and methanol.

Having generally described the invention, the following examples aredesigned to instruct those skilled in the art of polymer processing onthe practice of adding gel-inhibitors to solutions comprised of EB and asolvent in order to control solution viscosity, inhibit time togelation, maintain particle and gel free solutions, and to form films,fibers, coatings and other articles, which may be further treated toimpart electrical conductivity.

EXAMPLE 1

A solution of 0.600 g (8.44×10⁻³ mole) of pyrrolidine (Py) combined with0.490 g of NMP was heated to 68° C. for about 10 min.; 0.305 g(8.43×10⁻⁴ mole) of EB (21% w/w) were then added to the hot solutionwith stirring. This gave a GI/EB molar ratio of 10. The resultingmixture was stirred for several minutes. Most of the EB dissolved. Afterheating for an additional 5 min. a homogenous solution formed, and adense film was produced by spreading the solution onto a glass platewhich was then thermally annealed at 120° C. for approximately 2 h. toremove the casting solution. Another wet film was formed by spreading aportion of the solution onto a glass plate and immediately immersing itin a water bath whereupon the polymer precipitated to form a film. Bothfilms were found to be very brittle before acid doping treatments, andthe thermally annealed film was noticed to be more of a powder than afilm when removed from the glass substrate by means of razor blade. Thisis in contrast to the same preparation performed with 1.02 g of NMP and0.082 g (1.16×10⁻³ mole) of pyrrolidine, and 0.304 g of EB (GI/EB molarratio=1.4) where a flexible, thermally cured dense film was obtained.This example clearly shows that a gel inhibitor such as pyrrolidine isnot a cosolvent for polyaniline, and that, while providing enhancedsolubility, a molar excess of Py, beyond the claims of the presentinvention, adversely effects the mechanical properties of the film orcoating, most likely through physical degradation of the polymer.

EXAMPLE 2

To a solution of 0.621 g (6.14×10⁻³ mole) of dipropylamine and 0.512 gof NMP, which was heated at 68° C. for about 10 min., 0.305 g (8.47×10⁻⁴mole) of EB was added (GI/EB=7.25), and the resulting solution stirredfor several minutes. A pasty EB powder which did not dissolve theobserved product was formed. Upon further heating for approximately 30min., no solubility improvement was observed. Thus, a 20% w/w flowableliquid of EB was not possible to prepare under these conditions. This isto be contrasted to a solution of 1.02 g of NMP, 0.305 g (8.47×10⁻⁴mole) of EB, and 0.108 g (1.07×10⁻³ mole) of dipropylamine (GI/EB=1.26)which, after the same heating procedure described above, generated a(20% w/w) polyaniline solution which could be formed into flexible filmsby thermal annealing or IP, and when doped in 1 N HCl gave highconductivity (>1 S/cm). This example shows that gel inhibitors such asdipropylamine are not cosolvents for polyaniline, but in fact, atelevated concentrations they are nonsolvents for the polymer.

Similarly, to a solution of 0.512 g of NMP and 0.550 g (3.95×10⁻³ mole)of decahydroquinoline, which was heated to 68° C. for about 10 min.,0.305 g (8.43×10⁻⁴ mole) of EB was added and the resulting mixture(GI/EB=4.72) stirred for several minutes. A clear solution was observed.The solution was heated for an additional 5 min., but a pastyprecipitate and/or gel was observed. Upon attempting to cast this gelinto a dense film, cracks were observed in the resulting film. This isin contrast to the same procedure applied to 1.0 g of NMP and 0.16 g(1.15×10⁻³ mole) of decahydroquinoline, where a 20% w/w polyanilinesolution (GI/EB=1.36) was observed to be stable against gel formationfor more than 10 min. at 68° C. This example shows the sensitivity of GIconcentration to resulting gelation time and film quality.

EXAMPLE 3

The following secondary amines, which are themselves good gel inhibitorsas described in the preferred embodiments of the present invention, wereused as solvents in an attempt to make ˜20% (w/w) flowable liquidsolutions with EB at 60° C.: 1) 22 mg (6.1×10⁻⁵ mole) of EB was added to80 mg (7.8×10⁻⁴ mole) of hot dipropylamine (GI/EB=12.8) with vigorousmixing, but the dipropylamine only wet and swelled the EB powder; 2) 20mg (5.5×10⁻⁵ mole) of EB was added to 79 mg (6.1×10⁻⁴ mole) ofdibutylamine (GI/EB=11.1), but the dibutylamine only wet and swelled theEB powder; 3) 22 mg (6.1×10⁻⁵ mole) of EB was added to 79 mg (9.5×10⁻⁴mole) of 1,2,3,6-tetrahydropyridine (GI/EB=15.6), it immediately gelledupon mixing with the EB powder; 4) 21 mg (5.2×10⁻⁵ mole) of EB was addedto 80 mg (7.1×10⁻⁴ mole) of heptamethyleneimine (GI/EB=12.2), but theheptamethyleneimine only wet and swelled the EB powder; and, 5) 19 mg(5.2×10⁻⁵ mole) of EB was added to 80 mg (6.9×10⁻⁴ mole) of2,6-dimethylmorpholine (GI/EB=1 3.3),but the 2,6-dimethylmorpholine onlywet and swelled the EB powder. These examples show that GI's are not bythemselves good solvents for the EB form of polyaniline. They alsoindicate that gel inhibitors are typically nonsolvents for EB at thehigher total solids content of the present invention. One exceptionfollows in the next example.

EXAMPLE 4

It might be expected that a bifunctional molecule containing both asecondary amine group (to complex with imine nitrogens of the polymer)and an amide group (to solvate the secondary amine groups of thepolymer) would be simultaneously a gel-inhibitor and a solvent, andhence dissolve >15% w/w high molecular weight EB. One such bifunctionalcompound is 1-acetylpiperazine. This molecule has a secondary amine andan amide functional group situated within its heterocyclic ringstructure. This bifunctionality allows not only good solvent solubilitycharacteristics, but it also provides the secondary amine structurecommon to gel inhibitors. Specifically, 1.186 g of 1-acetylpiperazinewas added to a 10 ml PTFE screw-cap vial and heated to 100° C. for 20min.; 308 mg of polyaniline was quickly added to this solvent withvigorous stirring for a few minutes. The solution became homogeneous,free from gel particles, in a short time. A thermally annealed film andan IP film were prepared in the usual fashion. Both films were flexibleand of high quality, and had high conductivities after doping in 1 NHCl. This example shows that such bifunctional compounds can be usedadvantageously to dissolve EB at concentrations >20% w/w. However, thesesolutions had short gelation times which were more advantageously usedby the addition of small amounts of other gel inhibitors.

EXAMPLE 5

Table 2 shows the results of 14 different experiments using differentgel-inhibitor compounds prepared with NMP solutions containing EB in therange of 19 to 21% (w/w), and variable amounts of GI to EB ranging from0.7 to 2.5 (2.5 to 5.0 in the case of 2-methylaziridine). Table 2 alsolists the subsequent doping effects on the conductivities (s=S/cm) andmechanical integrity of these thermally annealed films. The filmsindicated "Very Brittle" could not be measured for bulk conductivity.These results show that the physical properties (conductivity andmechanical properties) of thermally annealed films are sensitive to themixing stoichiometry of the gel inhibitor relative to the EB repeatunit. In all instances, except for 2-methylaziridine, there is asignificant decrease of bulk conductivity with increasing molar ratiosof GI to EB. Similarly, at higher ratios of GI/EB, the heterocyclicamines tend to decrease the resulting mechanical properties of thethermally annealed films after acid doping, while the linear aminesexhibit conductivity decreases but still preserve their mechanicalintegrity. This example once again shows that gel inhibitors are notcosolvents and that acid doped film and coating properties are quitesensitive to the molar ratio of GI to EB.

                  TABLE 2                                                         ______________________________________                                                    Mole Ratio  s        Mechanical                                     Gel Inhibitor (GI) GI/EB (S/cm) Property                                    ______________________________________                                        Pyrrolidine 1.3         3.1 × 10.sup.-2                                                                  F                                               2.5 2.5 × 10.sup.-5 B                                                  2 Methylaziridine 2.5 15   F                                                   5.0  3.5 B                                                                   (S)-(+) Pyrrolidine-2-  0.72 2.8 × 10.sup.-3 F                          methanol 1.4 NM VB                                                            3-Pyrroline 1.4 2.8 × 10.sup.-4 F                                        2.8 NM VB                                                                    3-Pyrrolidinol 1.4 7.0 × 10.sup.-5 F                                     2.8 NM VB                                                                    Dipropylamine 1.3 30.0 F                                                       2.8 3.2 × 10.sup.-2 F                                                  Dibutylamine 1.2 37.5 F                                                         1.69 4.2 × 10.sup.-2 F                                              ______________________________________                                         NM = Not Measureable                                                     

EXAMPLE 6

Table 3 presents a summary of the results from 60 "quick survey"experiments in which variable quantities of gel inhibitors were added toNMP solutions to dissolve ˜300 mg (8.3×10⁻⁴ mole) of EB as describedabove. In all cases, the concentration was generally greater than 20%(w/w), except for the (S)-(+)-2-(methoxymethyl)-pyrrolidine entry, whereonly 30 mg (8.3×10⁻⁵ mole) of polyaniline was used due to the limitedavailability of this GI. The results from Table 3 show the differencesin measured conductivity between the HCl acid-doped thermally annealedfilms and HCl doped IP films formed by coagulating the wet film castingsolutions in a nonsolvent (water) bath.

In general, Table 3 data shows that the IP films have higherconductivities than do the thermally cured dense films, and theresulting conductivities can range from 0 to 5 orders of magnitude indifference. These results suggest that IP leads to effective removal ofthe residual GI by solvent exchange with the water bath. The"brittleness" found for the IP films is a consequence of theinterconnecting pore structures observed by scanning electron microscopy(SEM). In a series of separate experiments, it was discovered that theaddition of LiCl salts to the water coagulation bath leads to anoninterconnected, closed-cell, pore morphology which yields moremechanically robust and nonbrittle films. Modifications of the physicalproperties for thermally annealed and IP films and coatings can beachieved by manipulating: 1. The total mass of polymer in the solutionat a constant GI/EB ratio, 2. Varying the dielectric properties of thenonsolvent used for the coagulation bath, e.g., adding salts, and 3.Varying the nature of the acid used for doping the polymer, e.g.,organic acids vs. inorganic acids.

                  TABLE 3                                                         ______________________________________                                                           Conductivity of                                                                          Conductivity of                                                                        Molar                                    Solvent  the Thermally the Immersion Ratio                                    (NMP)  Annealed Precipitated of                                               (g) Gel Inhibitor (g) Film (S/cm) Film (S/cm) GI/EB                         ______________________________________                                        1.025 2-Methylaziridine                                                                          15.0 (F)    3.4 (SF)                                                                              2.54                                      0.120                                                                        1.02 Azitidine 10.sup.-5 (B) NA 1.9                                            0.090                                                                        1.02 Pyrrolidine   4 × 10.sup.-2 (F) 0.11 (SF) 1.39                      0.082                                                                        1.025 Hexamethylene-  3.7 × 10.sup.-3 (F)  5.1 (SF) 1.26                 imine                                                                         0.104                                                                        1.034 Heptamethylene- 5.73 × 10.sup.-2  2.5 (SF) 1.11                    imine (F)                                                                     0.104                                                                        1.031 3-Pyrroline  2.8 × 10.sup.-4 (F)   2 × 10.sup.-2 1.40        0.080  (SF)                                                                  1.021 3-Pyrrolidinol   7 × 10.sup.-5 (F) 4.37 × 10.sup.-2                                              1.40                                      0.101  (SF)                                                                  1.051 (S)-(+)-pyrrolidine-  1.3 × 10.sup.-3 (F) 0.58 (SF) 0.72                                                 2-methanol                              0.060                                                                        1.02 (R)-(-)-pyrrolidine-  2.8 × 10.sup.-3 (F) 0.25 (SF) 0.72                                                  2-methanol                              0.060                                                                        1.02 4-Ethyl-2-methyl-  0.10 (F) NA 1.54                                       (3-methylbutyl)-                                                              oxazolidine                                                                   0.237                                                                        1.02 (S)-(+)- NM  1.8 × 10.sup.-2 (B) 1.47                               (Anilinomethyl)-                                                              pyrrolidine                                                                   0.215                                                                        1.03 1,3,3-Trimethyl-6-  1.1 × 10.sup.-4 (F) 0.14 (B) 1.53                                                     azabicyclo[3,2,1]-                      octane                                                                        0.195                                                                        0.110 (S)-(+)-2-  1.1 × 10.sup.-4 (F)  8.5 (B) 1.57                      (Methoxymethyl)-                                                              pyrrolidine                                                                   0.015                                                                        1.075 Indoline  5.5 × 10.sup.-5 (F) 0.54 (B) 1.50                        0.148                                                                        1.031 Thiomorpholine  6.4 × 10.sup.-1 (F)  2.2 × 10.sup.-2                                             (B) 1.89                                  0.162                                                                        0.98 Decahydroquinoline  0.17 (F) 12.5 (F) 1.39                                0.160                                                                        1.004 2,5-Dimethyl-  7.4 × 10.sup.-3 (F)   4 × 10.sup.-2                                               (B) 1.28                                  morpholine                                                                    0.122                                                                        1.029 Diethylamine 28.2 (F) 14.0 (B) 1.43                                      0.087                                                                        1.029 Dicyclohexyl-amine 78.0 (F) 22.0 (B) 1.36                                0.205                                                                        1.048 Dipropylamine   30 (F) 12.5 (B) 1.29                                     0.108                                                                        1.024 Dibutylamine 37.5 (F) 11.1 (B) 1.16                                      0.124                                                                        1.032 N-Methylhexyl-  1.0 (F)  1.2 (SF) 1.30                                   amine                                                                         0.124                                                                        1.05 1-Aza-15-crown-5  3.0 (F) 21.3 (SF) 1.36                                  0.248                                                                        1.064 1,4-Dioxa-8-  1.5 × 10.sup.-2 (F)  7.5 × 10.sup.-2                                               (F) 1.31                                  azaspirof[4.5]-                                                               decane                                                                        0.155                                                                        1.026 1,4,5,6-Tetrahydro-  4.2 × 10.sup.-2 (F)  3.9 (SF) 1.61                                                  pyrimidine                             1.023 1,2,3,6-Tetrahydro-  4.2 × 10.sup.-3 (F) 0.33 (SF) 1.41                                                  pyridine                               1.025 3,5-Dimethyl-  2.4 × 10.sup.-3 (F) 1.53 (SF) 1.63                  pipendine                                                                    1.020 3,3-Dimethyl-  9.3 × 10.sup.-4 (F) 0.11 (SF) 1.48                  piperidine                                                                    0.118                                                                        1.558 Morpholine  1.2 × 10.sup.-3 (F) 0.18 (SF) 1.25                     0.110                                                                        1.038 Piperidine  2.6 × 10.sup.-5 (F) 0.16 (SF) 2.3                      0.112                                                                      ______________________________________                                         NA = not available                                                       

The data from Table 3 show that there are many types of gel-inhibitors,which when used in the preferred concentration ranges of the presentinvention, may be preferentially employed to dissolve greater than 20%of high molecular weight EB. These solutions can be advantageously usedto fabricate thermally annealed free-standing films or coatings that maybe rendered electrically conductive by immersion in an acid. Similarly,these solutions can be used advantageously to fabricate articles such asinterconnecting and noninterconnecting porous articles by IP intononsolvents.

EXAMPLE 7

FIG. 3 plots the data for gelation time versus the molar ratio ofgel-inhibitor to EB repeat unit (GI's are 2-methylaziridine andpyrrolidine) for 20% w/w EB solutions in NMP at 60° C. It is clear thathigh GI/EB ratios lead to longer gelation times. For clarity, one suchsolution preparation is now described: 0.505 g of NMP and 79 mg of2-methylaziridine [Aldrich, 90%, (1.25×10⁻⁴ mole)] were mixed in a 10 mlPTFE screw-cap vial and heated at 60° C. for 5 min.; 154 mg of EB(4.3×10⁻⁴ mole) were then added to this solution (GI/EB=2.90), stirredvigorously for several minutes, and then returned to the oven at 60° C.for 5 min. The vial was removed after each of nine, 5 min. timeintervals, and vigorously stirred until a homogeneous, flowable liquidformed. The solution was then returned to the oven at 60° C. where itremained until it gelled. The gelation time was monitored from themoment the homogeneous EB solution formed until the time when thesolution would no longer flow. Gelation time was defined as the timewhen, after the sample vial was tilted to an angle of 180°, the liquidphase no longer flowed to the bottom of the container. Each of the2-methylaziridine and pyrrolidine solutions plotted in FIG. 3 wasprepared and analyzed in this fashion.

FIG. 3 shows that the different gel-inhibitors of the present inventionhave different effects on the gelation times, and that higher ratios ofGI/EB tend to give longer times to gelation. Much longer gelation timesoccur if such studies are carried out at lower temperatures. Forexample, the EB/NMP/2-MA solution described above gelled in 2.5 h. at60° C. When the same solution composition was prepared and stored in therefrigerator (˜2° C.) for more than 48 h., it remained a flowablegel-free liquid for this time interval.

FIG. 4 is a plot of thermally annealed film conductivity results versusthe molar ratio of gel-inhibitor to EB repeat unit (2-methylaziridineand pyrrolidine) used to prepare samples in NMP, all atconcentrations >20% EB w/w. The samples were prepared described aboveand the conductivities were measured at 20° C. by the four-point probemethod (See Vander Pauw, supra). It is clear that at higher GI/EBratios, reductions in thermally annealed film mechanical propertiesoccur. Additionally, certain GI's of the present invention, e.g.,pyrrolidine, exhibit substantially reduced bulk conductivities for filmsand coatings when compared with other GI's such as 2-methylaziridine atthe same GI/EB ratios. FIG. 4 shows that increasing the GI/EB ratio canin some instances decrease conductivity and mechanical integrity forthermally annealed films and coatings, while in other cases, onlymechanical properties are degraded.

EXAMPLE 8

A solution for spinning EB solid fibers was prepared as follows: 31.32 gof N-methyl-2-pyrrolidinone (NMP) was mixed with 4.879 g (7.9×10⁻² mole)of 2-methylaziridine [90%, 2-MA, Aldrich]. This mixture was placed in a60 ml glass jar with a teflon lined screw cap at 60° C. for 1 h., afterwhich 9.109 g (2.5×10⁻² mole) of EB was quickly added to this NMP/2-MAmixture (GI/EB=3.1), and vigorously stirred for a few minutes to wet thepolymer powder. The glass jar was tightly sealed and returned to theoven set at 100° C. for about 30 min. During this time, the EB/NMP/2-MAmixture was removed every 10 min. and vigorously stirred. After thistime, a flowable homogeneous liquid solution free from gel particlesformed. The concentration of EB in this solvent system was 20.1 wt %.

This EB solution was transferred to a hydraulic stainless steel cylinderand cooled to room temperature. A gear pump motor, fed by a nitrogen gasat 100 psi, was used to drive the EB fluid through 3/8 in. stainlesssteel tubing, and through a spinnerette (500 mm O.D.), at a pressure of250 to 1,000 psi. The polymer solution was extruded through a 1 in.air-gap directly into a water coagulation bath (0° C.) where the solventand GI were removed from the nascent polyaniline fiber by de-mixing andsolvent/nonsolvent exchange in the bath. The take-up speed was variedbetween 3 to 10 feet per min. The nascent fiber was continuously woundon a series of two water bath godets maintained at 15° C., and collectedon a bobbin by means of a Leesona Winder. The fibers were placed inwater extraction baths for 48 h. to remove residual solvent and driedunder dynamic vacuum. FIG. 5 shows a scanning electron micrograph of theresulting fiber. This example illustrates the utility of the solutionsof the present invention for solid fiber spinning.

The EB fiber was stretch-aligned in the following manner: A solderingiron was wrapped with a piece of teflon film and heated to 120° C. bymeans of a Variac temperature controller. The fiber was stretched acrossthe soldering iron tip under tension. As the heat softened the fiber, adraw stretch ratio of 3 to 5 times was obtained. This mechanicalstretching reduced the fiber diameter from 450 μm to about 100 μm. Themaximum draw ratio depends on the amount of residual plasticizingsolvent and the temperature of the hot tip. Overdrying the fiber mayreduce the drawing ratio due to the lower NMP content. The conductivityof the air-dried unstretched fiber was measured to be 1 to 5 S/cm andthe air-dried stretched fibers (about 4 times their unstretched length)had a conductivity greater than 20 S/cm. This example shows that theconductivity of fibers can be increased through stretch alignment whichleads to increased electronic mobility.

Six inch segments of the stretched and unstretched EB fiber wereimmersed in 400 ml of their respective aqueous acid solutions for 48 h.They were removed from the doping solution, dried under dynamic vacuumfor another 48 h., and their conductivity measured. The acid solutionsused for doping the solid fibers were: 1.5 N HCl, 1N acetic acid, and anaqueous solution of benzenephosphinic acid (BPA) (pH=-0.37). Thedesignation SF means somewhat flexible and is used if the fiber can bebent more than 90° without breaking, but cannot be bent more than 180°.These results are shown in Table 4 hereof.

                  TABLE 4                                                         ______________________________________                                                                     Benzene                                              Acetic phosphinic                                                           Acid HCl Acid acid Undoped                                                  ______________________________________                                        Conductivity of the                                                                       4.8    5.5       8.3    Insulator                                   stretched fiber with (B) (F) (SF) (F)                                         a draw ratio of 4                                                             Conductivity of the 0.31 0.71 0.049 Insulator                                 unstretched fiber (SF) (F) (SF) (F)                                         ______________________________________                                    

The conductivity of a stretch aligned fiber is generally 1 to 2 ordersof magnitude greater than that for an unstretched fiber. From thisexample one may observe that: (a) stretch-alignment of fibers increaseselectronic mobility; and (b) organic acids have better mechanicalproperties in the doped fibers.

EXAMPLE 9

A mixture of 1.022 g of 1-acetyl-2-piperidone and 160 mg of2-methylaziridine (2.52×10⁻³ mole) was heated at 80° C. for 15 min.,after which 306 mg (8.45×10⁻⁴ mole) of EB (GI/EB=2.98) was rapidly addedto this solution with vigorous stirring. The sample was returned to theoven at this temperature until the homogeneous flowable liquid solutionformed. The solution was applied to the surface of a 4 in.×4 in. glassslide and then thermally annealed at 120° C. for 60 min. The resultingfilm was immersed in water, and after a few minutes, it delaminated fromthe glass surface. The hot pin described in Example 8 was used at 120°C. to mechanically draw the film to 2.6 times its original length. Theconductivity of the doped, unstretched film was 20.5 S/cm and theconductivity of the stretched film was 50.3 S/cm. This Example showsthat films formed by the solutions of the present invention can bemechanically stretched to increase electronic mobility and increaseconductivity.

EXAMPLE 10

Table 5 shows the results from a quick screening of solvents observed towork with the gel-inhibitors of the present invention randomly chosenfor this study. By way of example, 52 mg of 3-pyrrolidinol (6.00×10⁻⁴mole) was mixed with 508 mg of N,N-dimethyacetamide and heated at 60° C.for 5 min., after which 156 mg of EB (4.31×10⁻⁴ mole) was added to thismixture (GI/EB=1.39). The solution stirred vigorously for 1 min. and,returned to the oven for 10 min. until homogeneous flowable liquidsolution formed. All the examples that are listed in Table 5 have an EBconcentration of >20% w/w. Thermally annealed films were obtained byevaporating the solvent from the cast wet film at 120° C. for 1 h. Thefilms were immersed in 1 N HCl for several hours, air dried, andmeasured for respective conductivities.

                  TABLE 5                                                         ______________________________________                                                                 Conductivity                                             (S/cm) Molar                                                                  and Mechanical Ratio                                                        Solvent Gel Inhibitor Properties GI/EB                                      ______________________________________                                        N,N-Dimethy-                                                                              3-Pyrrolidinol                                                                             6.0 × 10.sup.-3                                                                    1.39                                        acetamide  (F)                                                                Dimethylsulfoxide 2-Methylaziridine 13.5 2.9                                    (F)                                                                         N-Methyl-2- Diethylamine 28.2 1.43                                            pyrrolidinone  (F)                                                            1-Methyl-2-piperidone 2-Methyaziridine 20.5 3.0                                 (F)                                                                         Hexamethylphosphor 2,6-Dimethyl- 5.6 × 10.sup.-2 1.31                   amide morpholine (F)                                                          N-Ethyl-2- Dipropylamine 3.2 × 10.sup.-2 1.38                           pyrrolidinone  (F)                                                            N,N-Dimethyl- 3-Pyrroline  3.14 × 10.sup.-2 1.49                        propionamide  (B)                                                           ______________________________________                                    

This Example shows that new solvent systems can readily be foundaccording to the teachings of the present invention. In fact, thefollowing solvents were also found to generate films exhibitingdesirable properties: 1-cyclohexyl-2-pyrrolidinone, N-methylcaprolactam,1,5-dimethyl-2-pyrrolidinone,2-pyrrolidinone,1,3-dimethyl-2-imidazolidinone,1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, 1-methyl-2-pyridone,1-acetylpyrrolidine, 1-acetylpiperidine, 1-acetylpiperazine,4-acetylmorpholine, 1-acetyl-3-methylpiperidine,N,N,N',N'-tetramethyurea, tetramethylene sulfoxide, δ-valerolactam, N,N,2-trimethylpropionamide, and mixtures thereof.

The foregoing description of the invention has been presented forpurposes of illustration and description and is not intended to beexhaustive or to limit the invention to the precise form disclosed, andobviously many modifications and variations are possible in light of theabove teaching. The embodiments were chosen and described in order tobest explain the principles of the invention and its practicalapplication to thereby enable others skilled in the art to best utilizethe invention in various embodiments and with various modifications asare suited to the particular use contemplated. It is intended that thescope of the invention be defined by the claims appended hereto.

What is claimed is:
 1. A method for preparing solutions having between15% and 30% by weight of (M_(w))>120,000, (M_(n))>30,000 emeraldine baseform of polyaniline, which comprises the steps of: a. mixing a solventfor polyaniline with a secondary amine such that the molar ratio ofsecondary amine to polyaniline tetramer repeat unit is between 0.1 and5.0, forming thereby a solution; and b. dissolving the polyaniline inthe solution thus prepared.
 2. The method for preparing solutions havingbetween 15% and 30% by weight of (M_(w))>120,000, (M_(n))>30,000emeraldine base form of polyaniline as described in claim 1, wherein themolar ratio of secondary amine to polyaniline tetramer repeat unit isbetween 0.5 and
 3. 3. The method for preparing solutions having between15% and 30% by weight of (M_(w))>120,000, (M_(n))>30,000 emeraldine baseform of polyaniline as described in claim 1, wherein the molar ratio ofsecondary amine to polyaniline tetramer repeat unit is between 1 and 2.4. The method for preparing solutions having between 15% and 30% byweight of (M_(w))>120,000, (M_(n))>30,000 emeraldine base form ofpolyaniline as described in claim 1, wherein the solvent is chosen fromthe group consisting of: N-methyl-2-pyrrolidinone,N-ethyl-2-pyrrolidinone, 1-cyclohexyl-2-pyrrolidinone,1-methyl-2-piperidone, N-methylcaprolactam,1,5-dimethyl-2-pyrrolidinone, 2-pyrrolidinone,1,3-dimethyl-2-imidazolidinone,1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, 1-methyl-2-pyridone,1-acetylpyrrolidine, 1-acetylpiperdine, 1-acetylpiperazine,4-acetylmorpholine, 1-acetyl-3-methylpiperidine,N,N-dimethylpropionamide, N,N,N',N'-tetramethyurea,N,N-dimethylacetamide, dimethylsulfoxide, tetramethylene sulfoxide,N-hexamethylphosphoramide, δ-valerolactam, N,N, 2-trimethylpropionamide,and mixtures thereof.
 5. The method for preparing solutions havingbetween 15% and 30% by weight of (M_(w))>120,000, (M_(n))>30,000emeraldine base form of polyaniline as described in claim 1, wherein thesecondary amines are selected from the group consisting of:2-methylaziridine, azetidine, pyrrolidine, piperidine,hexamethyleneimine, heptamethyleneimine, 3-pyrroline, 3-pyrrolidinol,(R)-(-)-pyrrolidine-2-methanol, (S)-(+)-pyrrolidine-2-methanol,4-ethyl-2-methyl-(3methylbutyl)oxazolidine,(S)-(+)-(anilinomethyl)pyrrolidine,1,3,3-trimethyl-6azabicyclo[3,2,1]octane, (S)-(+)-2(methoxymethyl)pyrrolidine, indoline, thiomorpholine, decahydroquinoline,2,6-dimethylmorpholine, diethylamine, dicyclohexylamine, dipropylamine,dibutylamine, N-mMethylhexylamine,1-aza-15-crown-5,1,2,3,6-tetrahydropyridine, 1,4,5,6-tetrahydropyrimidine,1,4-dioxa-8-azaspiro [4.5]-decane, 3,3-dimethylpiperidine, morpholine,and 3,5-dimethylpiperidine, and mixtures thereof.
 6. A solution havingbetween 15% and 30% by weight of (M_(w))>120,000, (M_(n))>30,000emeraldine base form of polyaniline, which comprises: a solvent selectedfrom the group consisting of: N-methyl-2-pyrrolidinone,N-ethyl-2-pyrrolidinone, 1-cyclohexyl-2-pyrrolidinone,1-methyl-2-piperidone, N-methylcaprolactam,1,5-dimethyl-2-pyrrolidinone,2-pyrrolidinone,1,3-dimethyl-2-imidazolidinone,1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone,1-methyl-2-pyridone, 1-acetylpyrrolidine, 1-acetylpiperidine,1-acetylpiperazine, 4-acetylmorpholine, 1-acetyl-3-methylpiperidine, N,N-dimethylpropionamide, N,N,N',N'-tetramethyurea, N,N-dimethylacetamide,dimethylsulfoxide, tetramethylene sulfoxide, N-hexamethylphosphoramide,δ-valerolactam, N,N, 2-trimethylpropionamide, and mixtures thereof; asecondary amine such that the molar ratio of secondary amine topolyaniline tetramer repeat unit is between 0.1 and 5.0; and a chosenweight of polyaniline.
 7. The solution having between 15% and 30% byweight of (M_(w))>120,000, (M_(n))>30,000 emeraldine base form ofpolyaniline as described in claim 6, wherein the secondary amine isselected from the group consisting of: 2-methylaziridine, azetidine,pyrrolidine, piperidine, hexamethyleneimine, heptamethyleneimine,3-pyrroline, 3-pyrrolidinol, (R)-(-)-pyrrolidine-2-methanol,(S)-(+)-pyrrolidine-2-methanol,4-ethyl-2-methyl-(3-methylbutyl)oxazolidine,(S)-(+)-(anilinomethyl)pyrrolidine,1,3,3-trimethyl-6-azabicyclo[3,2,1]octane, (S)-(+)-2 (methoxymethyl)pyrrolidine, indoline, thiomorpholine, decahydroquinoline,2,6-dimethylmorpholine, diethylamine, dicyclohexylamine, dipropylamine,dibutylamine, N-methylhexylamine, 1-aza-15-crown-5,1,2,3,6-tetrahydropyridine, 1,4,5,6-tetrahydropyrimidine,1,4-dioxa-8-azaspiro[4.5]-decane, 3,3-dimethylpiperidine, morpholine,and 3,5-dimethylpiperidine, and mixtures thereof.
 8. The solution havingbetween 15% and 30% by weight of (M_(w))>120,000, (M_(n))>30,000emeraldine base form of polyaniline as described in claim 6, wherein themolar ratio of secondary amine to polyaniline tetramer repeat unit isbetween 0.5 and
 3. 9. The solution having between 15% and 30% by weightof (M_(w))>120,000, (M_(n))>30,000 emeraldine base form of polyanilineas described in claim 6, wherein the molar ratio of secondary amine topolyaniline tetramer repeat unit is between 1 and
 2. 10. A method forpreparing solutions having between 15% and 30% by weight of(M_(w))>120,000, (M_(n))>30,000 emeraldine base form of polyaniline,which comprises the step of dissolving a chosen amount of polyaniline ina bifunctional solvent therefor having both an amide group and asecondary amine group, forming thereby a solution.
 11. The method forpreparing solutions having between 15% and 30% by weight of(M_(w))>120,000, (M_(n))>30,000 emeraldine base form of polyaniline asdescribed in claim 10, further comprising the step of heating thesolvent before said step of dissolving the polyaniline.
 12. The methodfor preparing solutions having between 15% and 30% by weight of(M_(w))>120,000, (M_(n))>30,000 emeraldine base form of polyaniline asdescribed in claim 10, wherein the bifunctional solvent includes1-acetylpiperazine.
 13. A solution having between 15% and 30% by weightof (M_(w))>120,000, (M_(n))>30,000 emeraldine base form of polyaniline,which comprises a solution of a chosen amount of polyaniline in abifunctional solvent therefor having both an amide group and a secondaryamine group.
 14. The solution having between 15% and 30% by weight of(M_(w))>120,000, (M_(n))>30,000 emeraldine base form of polyaniline asdescribed in claim 13, wherein the bifunctional solvent includes1-acetylpiperazine.